US10173069B2 - Medical device fixation - Google Patents

Abstract

A fixation device configured to anchor an implantable medical device within a patient includes a temporary biodegradable fixation mechanism configured to secure the device after implantation until the temporary fixation mechanism biodegrades and a chronic fixation mechanism configured to promote tissue growth that secures the device to tissue of the patient before the temporary fixation mechanism biodegrades.

Description

This application claims the benefit of U.S. Provisional Patent Application No. 61/591,051, filed Jan. 26, 2012, the entire content of which is incorporated herein by reference.

TECHNICAL FIELD

The disclosure relates to medical devices and, more particularly, fixation of medical devices.

BACKGROUND

A variety of implantable medical devices for delivering a therapy and/or monitoring a physiological condition have been clinically implanted or proposed for clinical implantation in patients. Implantable medical devices may deliver electrical stimulation or pharmacologic therapy to, and/or monitor conditions associated with, the heart, muscle, nerve, brain, stomach or other organs or tissue, as examples. Some implantable medical devices may employ one or more elongated electrical leads carrying stimulation electrodes, sense electrodes, and/or other sensors. Implantable medical leads may be configured to allow electrodes or other sensors to be positioned at desired locations—either physically, or virtually (enabled/disabled electronically)—for delivery of stimulation or sensing. For example, electrodes or sensors may be carried at a distal portion of a lead. A proximal portion of the lead may be coupled to an implantable medical device housing, which may contain circuitry such as stimulation generation and/or sensing circuitry. Other implantable medical devices may be leadless and include, for example, one or more electrodes (e.g., sense and/or stimulation electrodes) on an outer surface of the medical device.

Implantable medical devices, such as cardiac pacemakers or implantable cardioverter-defibrillators, for example, provide therapeutic electrical stimulation to the heart via electrodes carried by one or more implantable leads. The electrical stimulation may include signals such as pulses or shocks for pacing, cardioversion or defibrillation. In some cases, an implantable medical device may sense intrinsic depolarizations of the heart, and control delivery of stimulation signals to the heart based on the sensed depolarizations. Upon detection of an abnormal rhythm, such as bradycardia, tachycardia or fibrillation, an appropriate electrical stimulation signal or signals may be delivered to restore or maintain a more normal rhythm. For example, in some cases, an implantable medical device may deliver pacing pulses to the heart of the patient upon detecting tachycardia or bradycardia, and deliver cardioversion or defibrillation shocks to the heart upon detecting tachycardia or fibrillation.

SUMMARY

In general, this disclosure is directed to fixation devices for implantable medical devices, which include a temporary biodegradable fixation mechanism configured to secure the device after implantation until the temporary fixation mechanism degrades and a chronic fixation mechanism configured to promote tissue growth that secures the device to the tissue of the patient after the temporary fixation mechanism biodegrades. Advantages of examples according to this disclosure may include reducing the size or “footprint” of a permanent fixation system, thereby suiting the structure better to the surrounding anatomy of an implant site, promoting a less invasive chronic milieu, higher safety, and greater reliability.

In one example, a fixation device for an implantable medical device (IMD). The fixation device includes a temporary fixation mechanism and a chronic fixation mechanism, both of which are configured to be connected to the IMD. The chronic fixation mechanism is configured to be connected to a first side of the IMD. The temporary fixation mechanism includes a biodegradable material and is configured to anchor the IMD within a blood vessel of a patient after implantation until the temporary fixation mechanism biodegrades. The chronic fixation mechanism is configured to promote tissue growth that anchors the IMD within the blood vessel before the temporary fixation mechanism biodegrades. The temporary fixation mechanism is configured to anchor the IMD within the blood vessel such that the first side of the IMD including the chronic fixation mechanism is arranged against endothelium of the blood vessel.

In another example, an implantable medical device (IMD) includes a body and a fixation device connected to the body of the IMD. The fixation device includes a temporary fixation mechanism and a chronic fixation mechanism. The temporary fixation mechanism includes a biodegradable material and is configured to anchor the IMD within a blood vessel of a patient after implantation until the temporary fixation mechanism biodegrades. The chronic fixation mechanism is connected to a first side of the body and configured to promote tissue growth that anchors the IMD within the blood vessel of the patient before the temporary fixation mechanism biodegrades. The temporary fixation mechanism is configured to anchor the IMD within the blood vessel such that the first side of the body including the chronic fixation mechanism is arranged against endothelium of the blood vessel.

Another example includes a method of securing an implantable medical device (IMD) within the body of a patient. The method includes arranging the IMD at a target location within a blood vessel of the patient, temporarily anchoring the IMD within the blood vessel with a temporary fixation mechanism including a biodegradable material and configured to secure the IMD within the blood vessel after implantation until the temporary fixation mechanism biodegrades, and chronically anchoring the IMD within the blood vessel with a chronic fixation mechanism connected to a first side of the IMD and configured to promote tissue growth that secures the IMD within the blood vessel before the temporary fixation mechanism biodegrades. The temporary fixation mechanism is configured to anchor the IMD within the blood vessel such that the first side of the IMD including the chronic fixation mechanism is arranged against endothelium of the blood vessel.

The details of one or more examples disclosed herein are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual drawing illustrating an example system that includes an implantable medical device (IMD) coupled to implantable medical leads and a leadless sensor.

FIG. 2 is a conceptual drawing illustrating in greater detail the example IMD, leads, and sensor ofFIG. 1 in conjunction with a heart.

FIGS. 3A and 3B are elevation and plan views, respectively, of an implantable sensor including an example fixation device according to this disclosure.

FIG. 4 is a flowchart illustrating an example method of securing an IMD with a fixation device according to this disclosure.

FIGS. 5A-5D are conceptual drawings illustrate the method ofFIG. 4 of securing an IMD within a vessel with the fixation device ofFIGS. 3A and 3B.

FIGS. 6A-6D are conceptual drawings illustrating a number of different example chronic fixation mechanisms.

FIG. 7 is a conceptual drawing illustrating an implantable sensor temporarily anchored with an example temporary fixation mechanism.

FIG. 8 is a plan view of an implantable sensor including another example fixation device according to this disclosure.

FIGS. 9A-9J are conceptual drawings illustrating a number of example temporary fixation mechanisms that may be employed in examples according to this disclosure.

DETAILED DESCRIPTION

The following examples are directed to techniques for securing medical devices within the body of a patient. Implantable medical devices (IMD) may be subject to various forces within the body of a patient, which may act to cause such devices to migrate from a particular implantation location and/or target tissue site for the implantable medical device. Fixation devices, including, e.g., barbs, tines, stents and other such structures, may be employed to help secure (or fix or anchor) medical devices within a patient and to help prevent or inhibit migration of the device. Forces within the body of a patient acting on an IMD and/or other devices attached to the IMD may also cause the IMD and/or attached devices to erode through tissue, which is undesirable, and may risk the integrity of fixation and/or of the implant site itself.

Increasing effort is being expended to design and market miniaturized medical devices. These include “leadless” pacemakers, “leadless” sensors, subcutaneously injectable monitoring devices (e.g. Medtronic's “Injectible Reveal”), and perhaps in the future, intravascularly injectable “micro-labs” or “nano-labs” that periodically, or even continually perform blood assays and report results back to an extracorporeal monitoring device that gathers the data, aggregates it, and reports it to a medical professional. These implantable “micro-labs” or “nano-labs” may also communicate with other devices chronically implanted in the body. One purpose of this may be for the micro-lab or nano-lab to communicate information to a chronically implanted device. Another purpose may be in order to take advantage of the ability of a larger implanted device to serve as a “repeater”, i.e. to re-transmit the signal over longer distances to an external monitoring system.

One of the challenges in implanting miniature devices within the cardiovascular system, including implanting leadless pacemakers and sensors, is fixation. Devices typically have an apparatus that holds them in place. For example, some pacing leads have tines or a helix at the tip to provide fixation. Inferior vena cava filters and other devices held within blood vessels employ a variety of stents to hold them in the vessel. One common feature of all the foregoing techniques is that the fixation device remains in the body permanently. The character and chronic placement of such fixation devices may produce a number of risks for a patient within whom the devices are implanted. For example, vascular stents, such as Nitinol stents or frames are known to fracture, posing a potential safety hazard. Second, stents and other fixation devices, such as tines or barbs, placed in certain vessels can erode through vessel walls. Third, stents are potentially thrombogenic. While stents can be coated with agents to reduce thrombosis, even coated stents may require anti-thrombotic therapy for some period of time, e.g., 12-months after implantation. Finally, metallic stents and other fixation devices, such as tines or barbs, may be unsafe for certain procedures, including, e.g., Magnetic Resonance Imagining (MRI).

In view of the foregoing challenges with current fixation devices that may be employed to secure miniature medical devices, examples according to this disclosure include a temporary fixation mechanism and a chronic fixation mechanism configured to be connected to an IMD. The temporary fixation mechanism includes a biodegradable material and is configured to anchor the IMD to tissue of a patient after implantation until the temporary fixation mechanism degrades. The chronic fixation mechanism is configured to promote tissue growth that secures the device to the tissue of the patient before the temporary fixation mechanism degrades. Example fixation devices according to this disclosure may be employed virtually anywhere in the vascular system, including within the chambers of the heart, but may prove especially useful in larger vessels, to eliminate the need for large stents or other large fixation mechanisms that could produce adverse effects over time. Additionally, examples according to this disclosure may be especially useful in the case of implanted devices, e.g. micro- or nano-sensing systems that are small compared to the fixation mechanism normally required to chronically anchor such devices within a vessel or cavity.

FIG. 1 is a conceptual diagram illustrating anexample system10 that may be used for sensing of physiological parameters ofpatient14 and/or to provide therapy toheart12 ofpatient14.Therapy system10 includesIMD16, which is coupled to leads18,20, and22, andprogrammer24.IMD16 may be, for example, an implantable pacemaker, cardioverter, and/or defibrillator that provides electrical signals toheart12 via electrodes coupled to one or more ofleads18,20, and22.Patient14 is ordinarily, but not necessarily, a human patient.

IMD16 may include electronics and other internal components necessary or desirable for executing the functions associated with the device. In one example,IMD16 includes one or more processors, memory, a signal generator, sensing module and telemetry modules, and a power source. In general, memory ofIMD16 may include computer-readable instructions that, when executed by a processor of the IMD, cause it to perform various functions attributed to the device herein. For example, a processor ofIMD16 may control the signal generator and sensing module according to instructions and/or data stored on memory to deliver therapy topatient14 and perform other functions related to treating condition(s) of the patient withIMD16.

The signal generator ofIMD16 may generate electrical stimulation that is delivered topatient12 via electrode(s) on one or more ofleads18,20, and22, in order to provide, e.g., cardiac sensing, pacing signals, or cardioversion/defibrillation shocks. The sensing module ofIMD16 may monitor electrical signals from electrode(s) on leads18,20, and22 ofIMD16 in order to monitor electrical activity ofheart12. In one example, the sensing module may include a switch module to select which of the available electrodes on leads18,20, and22 ofIMD16 are used to sense the heart activity. Additionally, the sensing module ofIMD16 may include multiple detection channels, each of which includes an amplifier, as well as an analog-to-digital converter for digitizing the signal received from a sensing channel for, e.g., electrogram signal processing by a processor of the IMD.

A telemetry module ofIMD16 may include any suitable hardware, firmware, software or any combination thereof for communicating with another device, such as programmer24 (FIG. 1). Under the control of a processor ofIMD16, the telemetry module may receive downlink telemetry from and send uplink telemetry toprogrammer24 with the aid of an antenna, which may be internal and/or external.

The various components ofIMD16 may be coupled to a power source, which may include a rechargeable or non-rechargeable battery. A non-rechargeable battery may be capable of holding a charge for several years, while a rechargeable battery may be inductively charged from an external device, e.g., on a daily or weekly basis.

Leads18,20,22 extend into theheart12 ofpatient14 to sense electrical activity ofheart12 and/or deliver electrical stimulation toheart12. In the example shown inFIG. 1, right ventricular (RV) lead18 extends through one or more veins (not shown), the superior vena cava (not shown), andright atrium26, and intoright ventricle28. Left ventricular (LV)coronary sinus lead20 extends through one or more veins, the vena cava,right atrium26, and into thecoronary sinus30 to a region adjacent to the free wall ofleft ventricle32 ofheart12. Right atrial (RA) lead22 extends through one or more veins and the vena cava, and into theright atrium26 ofheart12.

System10 also includesvascular sensor38.Sensor38 is implanted inpulmonary artery39. In one example,sensor38 is configured to sense blood pressure ofpatient14. For example,sensor28 may be arranged inpulmonary artery39 and be configured to sense the pressure of blood flowing from the right ventricle outflow tract (RVOT) fromright ventricle28 through the pulmonary valve topulmonary artery39.Sensor38 may therefore directly measure pulmonary artery diastolic pressure (PADP) ofpatient14. The PADP value is a pressure value that can be employed in patient monitoring. For example, PADP may be used as a basis for evaluating congestive heart failure in a patient. In other examples, however,sensor38 may be employed to measure blood pressure values other than PADP. For example,sensor38 may be arranged inright ventricle28 ofheart14 to sense RV systolic or diastolic pressure. Moreover, the placement ofsensor38 is not restricted necessarily to the pulmonary side of the circulation. In one example,sensor38 may be arranged in the systemic side of the circulation—e.g. in the left atrium, left ventricle, or aorta. Additionally,sensor38 may be arranged outside of the cardiovascular system, including, e.g., arrangingsensor38 in a renal vessel. In such examples,sensor38 may still be configured to communicate withIMD16 and/or with one or more electrodes or other sensors on leads18,20, or22. Arrangingsensor38 in the renal system may be appropriate, e.g., in a case in whichIMD16 is configured to treat heart failure by including some estimate of the degree of renal insufficiency in a patient. In one example according to this disclosure, a temporary fixation mechanism may be used to holdsensor38 to the epicardium ofheart12 ofpatient14, while a chronic fixation mechanism promotes tissue growth to chronically anchorsensor38 in that location.

In some examples,sensor38 includes a pressure sensor configured to respond to the absolute pressure insidepulmonary artery39 ofpatient14.Sensor38 may be, in such examples, any of a number of different types of pressure sensors. One form of pressure sensor that may be useful for measuring blood pressure inside a human heart is a capacitive pressure sensor. Another example pressure sensor is an inductive sensor. In some examples,sensor38 may also be a piezoelectric or piezoresistive pressure transducer. In other examples,sensor38 may include a fluid flow, optical, glucose, or a heart sound sensor.

In one example,sensor38 is a leadless pressure sensor including capacitive pressure sensing elements configured to measure blood pressure withinpulmonary artery39. As illustrated inFIGS. 1 and 2,sensor38 may be in wireless communication withIMD16, e.g., in order to transmit blood pressure measurements to the IMD.Sensor38 may employ, e.g., radio frequency (RF) or other telemetry techniques for communicating withIMD16 and other devices, including, e.g.,programmer24. In another example,sensor38 may include a tissue conductance communication (TCC) system by which the device employs tissue ofpatient14 as an electrically conductive communication medium over which to send and receive information to and fromIMD16 and other devices.

As described in greater detail below,sensor38 may include a fixation device according to this disclosure including a temporary biodegradable fixation mechanism and a tissue-growth promoting chronic fixation mechanism configured to secure the sensor withinpulmonary artery39 or to another target tissue site ifsensor38 is implanted at another location withinpatient14. In one example, the fixationdevice securing sensor38 includes a temporary fixation mechanism and a chronic fixation connected tosensor38. The temporary fixation mechanism includes a biodegradable material and is configured to anchorsensor38 withinpulmonary artery39 until the temporary fixation mechanism degrades. The chronic fixation mechanism is configured to promote tissue growth that securessensor38 withinpulmonary artery39, e.g. within the lumen of the artery and against the endothelium, before the temporary fixation mechanism degrades. For example, once the chronic fixation mechanism has completely anchoredsensor38 to the endothelium within the lumen ofpulmonary artery39, the temporary fixation mechanism may be designed to begin biodegrading in a substantially uniform, safe manner, leavingsensor38 anchored inpulmonary artery39 by tissue ingrowth facilitated by the chronic fixation mechanism. Example fixation devices according to this disclosure may be employed virtually anywhere in the vascular system, including within the chambers of the heart, but may prove especially useful in larger vessels, to eliminate the need for large stents or other large fixation mechanisms that could produce adverse effects over time.

Referring again toFIG. 1,system10 may, in some examples, additionally or alternatively include one or more leads or lead segments (not shown inFIG. 1) that deploy one or more electrodes within the vena cava or other vein. These electrodes may allow alternative electrical sensing configurations that may provide improved or supplemental sensing in some patients. Furthermore, in some examples,therapy system10 may include temporary or permanent epicardial or subcutaneous leads, instead of or in addition to leads18,20 and22. Such leads may be used for one or more of cardiac sensing, pacing, or cardioversion/defibrillation. In some examples,therapy system10 may include one or more leads or lead segments (not shown inFIG. 1) that deploy one or more electrodes within the systemic circulation (left atrium, left ventricle, artery), accessed trans-septally, or via an epicardial stick. These electrodes may allow alternative electrical sensing configurations that may provide improved or supplemental sensing in some patients.

IMD16 may sense electrical signals attendant to the depolarization and repolarization ofheart12 via electrodes (not shown inFIG. 1) coupled to at least one of theleads18,20,22. In some examples,IMD16 provides pacing pulses toheart12 based on the electrical signals sensed withinheart12. The configurations of electrodes used byIMD16 for sensing and pacing may be unipolar or bipolar.IMD16 may detect arrhythmia ofheart12, such as tachycardia or fibrillation ofventricles28 and32, and may also provide defibrillation therapy and/or cardioversion therapy via electrodes located on at least one of theleads18,20,22. In some examples,IMD16 may be programmed to deliver a progression of therapies, e.g., pulses with increasing energy levels, until a fibrillation ofheart12 is stopped.IMD16 detects fibrillation employing any of a number of known fibrillation detection techniques.

Programmer24 shown inFIG. 1 may be a handheld computing device, computer workstation, or networked computing device.Programmer24 may include electronics and other internal components necessary or desirable for executing the functions associated with the device. In one example,programmer24 includes one or more processors and memory, as well as a user interface, telemetry module, and power source. In general, memory ofprogrammer24 may include computer-readable instructions that, when executed by a processor of the programmer, cause it to perform various functions attributed to the device herein. Memory, processor(s), telemetry, and power sources ofprogrammer24 may include similar types of components and capabilities described above with reference to similar components ofIMD16.Programmer24 may also be a dedicated wireless system that communicates withIMD16 remotely, e.g., from the bedside table ofpatient14, while the patient sleeps.

In one example,programmer24 includes a user interface that receives input from a user. The user interface may include, for example, a keypad and a display, which may be a cathode ray tube (CRT) display, a liquid crystal display (LCD) or light emitting diode (LED) display. The keypad may take the form of an alphanumeric keypad or a reduced set of keys associated with particular functions.Programmer24 can additionally or alternatively include a peripheral pointing device, such as a mouse, via which a user may interact with the user interface. In some embodiments, a display ofprogrammer24 may include a touch screen display, and a user may interact withprogrammer24 via the display. It should be noted that the user may also interact withprogrammer24 remotely via a networked computing device. For example, a physician may communicate withIMD16, e.g. program the device by logging intoprogrammer24 from a remote location via the Internet, a cellular network, or other terrestrial or satellite-based communication network. In one example,programmer24 may be a fully automated monitoring base station for use in the home ofpatient14, with little or no capability for the patient or another user to provide input or programming toIMD16.

A user, such as a physician, technician, surgeon, electrophysiologist, or other clinician, may interact withprogrammer24 to communicate withIMD16. For example, the user may interact withprogrammer24 to retrieve physiological or diagnostic information fromIMD16. A user may also interact withprogrammer24 toprogram IMD16, e.g., select values for operational parameters of the IMD.

For example, the user may useprogrammer24 to retrieve information fromIMD16 regarding the rhythm ofheart12, trends therein over time, or arrhythmic episodes. As another example, the user may useprogrammer24 to retrieve information fromIMD16 regarding other sensed physiological parameters ofpatient14, such as intracardiac or intravascular pressure, activity, posture, respiration, or thoracic impedance. As another example, the user may useprogrammer24 to retrieve information fromIMD16 regarding the performance or integrity ofIMD16 or other components ofsystem10, such as leads18,20 and22, or a power source ofIMD16. In some examples, this information may be presented to the user as an alert.

The user may useprogrammer24 to program a therapy progression, select electrodes used to deliver electrical stimulation to heart12 (e.g., in the form of pacing pulses or cardioversion or defibrillation shocks), select waveforms for the electrical stimulation, or select or configure a fibrillation detection algorithm forIMD16. The user may also useprogrammer24 to program aspects of other therapies provided byIMD16, such as cardioversion or pacing therapies. In some examples, the user may activate certain features ofIMD16 by entering a single command viaprogrammer24, such as depression of a single key or combination of keys of a keypad or a single point-and-select action with a pointing device.

IMD16 andprogrammer24 may communicate via wireless communication, e.g. via telemetry modules in each of the devices using any number of known techniques. Examples of communication techniques may include, for example, low frequency or RF telemetry, but other techniques are also contemplated. In some examples,programmer24 may include a programming head that may be placed proximate to the patient's body near theIMD16 implant site in order to improve the quality or security of communication betweenIMD16 andprogrammer24.

FIG. 2 is a conceptualdiagram illustrating IMD16 and leads18,20 and22 oftherapy system10 in greater detail. Leads18,20,22 may be electrically coupled to a signal generator, e.g., stimulation generator, and a sensing module ofIMD16 viaconnector block34. In some examples, proximal ends ofleads18,20,22 may include electrical contacts that electrically couple to respective electrical contacts withinconnector block34 ofIMD16. In addition, in some examples, leads18,20,22 may be mechanically coupled toconnector block34 with the aid of set screws, connection pins, snap connectors, or another suitable mechanical coupling mechanism.

Each of theleads18,20,22 includes an elongated insulative lead body, which may carry a number of concentric coiled conductors separated from one another by tubular insulative sheaths. Other lead configurations may also be used.Bipolar electrodes40 and42 are located adjacent to a distal end oflead18 inright ventricle28. In addition,bipolar electrodes44 and46 are located adjacent to a distal end oflead20 incoronary sinus30 andbipolar electrodes48 and50 are located adjacent to a distal end oflead22 inright atrium26. In the illustrated example, there are no electrodes located inleft atrium36. However, other examples may include electrodes inleft atrium36.

Electrodes40,44 and48 may take the form of ring electrodes, andelectrodes42,46 and50 may take the form of extendable helix tip electrodes mounted retractably within insulative electrode heads52,54 and56, respectively. In other embodiments, one or more ofelectrodes42,46 and50 may take the form of small circular electrodes at the tip of a tined lead or other fixation element. Leads18,20,22 also includeelongated electrodes62,64,66, respectively, which may take the form of a coil. Each of theelectrodes40,42,44,46,48,50,62,64 and66 may be electrically coupled to a respective one of the coiled conductors within the lead body of its associatedlead18,20,22, and thereby coupled to respective ones of the electrical contacts on the proximal end ofleads18,20 and22.

In some examples, as illustrated inFIG. 2,IMD16 includes one or more housing electrodes, such ashousing electrode58, which may be formed integrally with an outer surface of hermetically-sealedhousing60 ofIMD16 or otherwise coupled tohousing60. In some examples,housing electrode58 is defined by an uninsulated portion of an outward facing portion ofhousing60 ofIMD16. Other division between insulated and uninsulated portions ofhousing60 may be employed to define two or more housing electrodes. In some examples,housing electrode58 comprises substantially all ofhousing60.Housing60 may enclose a signal generator that generates therapeutic stimulation, such as cardiac pacing pulses and defibrillation shocks, as well as a sensing module for monitoring the rhythm ofheart12

IMD16 may sense electrical signals attendant to the depolarization and repolarization ofheart12 viaelectrodes40,42,44,46,48,50,62,64 and66. The electrical signals are conducted toIMD16 from the electrodes via the respective leads18,20,22.IMD16 may sense such electrical signals via any bipolar combination ofelectrodes40,42,44,46,48,50,62,64 and66. Furthermore, any of theelectrodes40,42,44,46,48,50,62,64 and66 may be used for unipolar sensing in combination withhousing electrode58. The sensed electrical signals may be processed as an intracardiac electrogram (EMG) signal byIMD16.

Any combination ofelectrodes40,42,44,46,48,50,58,62,64 and66 may be considered a sensing configuration that has one or more electrodes. In some examples, a sensing configuration may be a bipolar electrode combination on the same lead, such aselectrodes40 and42 oflead18. In any sensing configuration, the polarity of each electrode in the sensing configuration may be configured as appropriate for the application of the sensing configuration.

In some examples,IMD16 delivers pacing pulses via bipolar combinations ofelectrodes40,42,44,46,48 and50 to cause depolarization of cardiac tissue ofheart12. In some examples,IMD16 delivers pacing pulses via any ofelectrodes40,42,44,46,48 and50 in combination withhousing electrode58 in a unipolar configuration. Furthermore,IMD16 may deliver cardioversion or defibrillation pulses toheart12 via any combination ofelongated electrodes62,64,66, andhousing electrode58.Electrodes58,62,64,66 may also be used to deliver cardioversion pulses, e.g., a responsive therapeutic shock, toheart12.Electrodes62,64,66 may be fabricated from any suitable electrically conductive material, such as, but not limited to, platinum, platinum alloy or other materials known to be usable in implantable defibrillation electrodes.

The configuration oftherapy system10 illustrated inFIGS. 1 and 2 is merely one example. In other examples, a therapy system may include epicardial leads and/or patch electrodes instead of or in addition to the transvenous leads18,20,22 illustrated inFIG. 1. Further,IMD16 need not be implanted withinpatient14. In examples in whichIMD16 is not implanted inpatient14,IMD16 may deliver defibrillation pulses and other therapies toheart12 via percutaneous leads that extend through the skin ofpatient14 to a variety of positions within or outside ofheart12.

In addition, in other examples, a therapy system may include any suitable number of leads coupled toIMD16, and each of the leads may extend to any location within or proximate toheart12. For example, other examples of therapy systems may include three transvenous leads located as illustrated inFIGS. 1 and 2, and an additional lead located within or proximate to leftatrium36. As another example, other examples of therapy systems may include a single lead that extends fromIMD16 intoright atrium26 orright ventricle28, or two leads that extend into a respective one of theright ventricle26 andright atrium26.

IMD16 andsensor38 may be configured to communicate with one another and function in conjunction with one another in a variety of ways. For example,IMD16 may receive sensor data fromsensor38 and store the data and/or transmit data toprogrammer24. Additionally,IMD16 may analyze data fromsensor38, e.g., for capture detection, tachyarrhythmia detection, or evaluation of cardiac performance parameters, such as contractility, or cardiac output. Cardiac performance parameters may be employed byIMD16 to adjust therapy parameters, such as CRT parameters, either by a user or automatically in a closed loop configuration.

FIGS. 3A and 3B are elevation and plan views, respectively, ofsensor38 includingexample fixation device100 withtemporary fixation mechanism102 andchronic fixation mechanism103.Sensor38 also includesbattery104, sensingelements106, andTCC electrodes108. In the example ofFIGS. 3A and 3B, sensingelements106 and other electronic components ofsensor38, e.g., a TCC system, is powered bybattery104. Sensingelements106 may include any suitable sensing elements for sensing a physiological parameter ofpatient14, such as, but not limited to capacitive sensing elements to measure internal pressures withinpatient14, including, e.g. blood pressure withinpulmonary artery39. In one example,battery104, sensingelements106, and other internal components ofsensor38 may be substantially fully encapsulated within an external housing, which, e.g., may be hermetically sealed to inhibit contact of body fluids with the components of the sensor and migration of chemicals within the sensor to the body ofpatient14.

Sensor38 may, in one example, communicate with, e.g.,IMD16 andprogrammer24 with a TCC system viaTCC electrodes108 arranged at opposite ends of the sensor. The TCC system ofsensor38 may employ tissue ofpatient14 as a communication medium over which information can be sent to and received fromIMD16 and other devices. In another example,sensor38 may employ, e.g., RF or other telemetry techniques for communicating withIMD16 and other devices, including, e.g.,programmer24.

Sensor38 includesfixation device100 according to this disclosure.Fixation device100 includestemporary fixation mechanism102 andchronic fixation mechanism103, both of which are connected to the housing ofsensor38. Temporary andchronic fixation mechanisms102,103, respectively, may be connected tosensor38 using a variety of techniques. For example,temporary fixation mechanism102 may be connected tosensor38 employing the fixation attachment mechanisms described in U.S. application Ser. No. 13/050,417, filed Mar. 17, 2011 and entitled “MEDICAL DEVICE FIXATION ATTACHMENT MECHANISM,” the entire content of which is incorporated herein by this reference. Additionally,chronic fixation mechanism103 may be connected tosensor38 using adhesives or, in one example, pinching one or more edges of the mechanism in a slot on the outer surface of the sensor. Other appropriate methods for connecting temporary andchronic fixation mechanisms102,103, respectively, tosensor38 are also contemplated for use in examples according to this disclosure.

Temporary fixation mechanism102 is fabricated from a biodegradable material and is configured to anchorsensor38 to tissue ofpatient14 after implantation untilchronic fixation mechanism103 facilitates sufficient tissue growth to chronically anchorsensor38, after which the temporary fixation mechanism may be configured to degrade. As noted above, in one example,sensor38 is implanted inpulmonary artery39 and configured to sense blood pressure ofpatient14, including, e.g., sensing the pressure of blood flowing from the right ventricle outflow tract (RVOT) fromright ventricle28 through the pulmonary valve topulmonary artery39 to measure pulmonary artery diastolic pressure (PADP) ofpatient14. Exampletemporary fixation mechanism102 includes an expandable and contractible structure, such as a stent or stent-like structure, formed from a filament that includes a contoured shape adapted for anchoringsensor38 within the lumen of a blood vessel or other chamber. In general, such an expandable structure may be expandable in a radial direction, although expansion in other directions is possible. Expandable structures may be self-expanding, or may be expanded by inflation of a balloon, as one example, or other means of applying force to the structure. Where the term stent is used herein, it should be interpreted to generally refer to an expandable and contractible structure that is configured to anchor an IMD to tissue of a patient, e.g. within the lumen of a blood vessel by applying force outward against the lumen walls, or, in other words, against the endothelium of the vessel.

In one example,temporary fixation mechanism102 includes a biodegradable stent configured to be connected to a first side ofsensor38 as illustrated inFIGS. 3A and 3B.Temporary fixation mechanism102 is configured to expand into engagement with the endothelium, within the lumen of a blood vessel, e.g. within the lumen ofpulmonary artery39 to push the side of sensor includingchronic fixation mechanism103 against the endothelium of the blood vessel.

In one example,temporary fixation mechanism102 includes a single filament contoured to form an expandable and contractible stent that anchorssensor38, or another IMD, within the body ofpatient14, e.g. within the lumen of a blood vessel such aspulmonary artery39. In another example,temporary fixation mechanism102 may include a number of filaments coupled to form an expandable and contractible stent that anchorssensor38 within the body ofpatient14.Temporary fixation mechanism102 is fabricated from a biodegradable material such that the fixation mechanism is configured to anchorsensor38 to tissue ofpatient14 after implantation until the temporary fixation mechanism degrades. In one example,temporary fixation mechanism102 is fabricated from a biodegradable material selected from the group consisting of polyesters, polyurethanes, and combinations thereof. In one example,temporary fixation mechanism102 is fabricated from a material comprising at least one of polyglycolic acid (PGA), polylactic acid (PLA), polydioxanone (PDS), polyanhydrides, trimethylene carbonate, polyhydroxybutyrate (PHB), polyhydroxyvalerate (PHV), polycaprolactone, polyorthoesters, polyaminoacids, polycyanocrylates, and polyphosphazenes. Additionally,temporary fixation mechanism102 may be fabricated from a copolymer of any two or more of the foregoing monomers and/or a blend of any two or more polymers listed above and their copolymers. In another example,temporary fixation mechanism102 is fabricated from one or more biodegradable metals, including, e.g., magnesium (Mg), magnesium alloys, iron (Fe), and iron alloys.

Temporary fixation mechanism102 andchronic fixation mechanism103 offixation device100 are configured to function in concert to anchorsensor38 within, e.g.,pulmonary artery39 ofpatient14. As such, in one example,temporary fixation mechanism102 is fabricated from a biodegradable material that is designed to degrade in a period of time that is sufficient to allow enough tissue growth tochronic fixation mechanism103 to securesensor38 in the lumen ofpulmonary artery39. The particular materials and relative amounts of each in the biodegradable material from whichtemporary fixation mechanism102 is formed may be varied, in order to vary the duration of time over which the fixation mechanism degrades. Additionally, the absolute amount of material that constitutestemporary fixation mechanism102 may also be varied to coordinate the degradation of the temporary fixation mechanism with the tissue growth intochronic fixation mechanism103.

In the example ofFIGS. 3A and 3B,chronic fixation mechanism103 includes a sheet of tissue growth promoting material configured to be connected to the IMD and configured to promote tissue growth into the material to secure the IMD to the tissue of the patient before the temporary fixation mechanism biodegrades.Chronic fixation mechanism103 is connected tosensor38 and overlays part of the outer surface of the body of the sensor. As illustrated inFIGS. 3A and 3B,chronic fixation mechanism103 includes a rectangular sheet of tissue growth promoting material defined by four edges. Two parallel and generally opposing edges ofchronic fixation mechanism103 are attached to the outer surface ofsensor38, e.g. using an adhesive and/or affixing the edges in a slot in the body of the sensor. In one example,chronic fixation mechanism103 may include a sheet of flexible fabric. In another example,chronic fixation mechanism103 may include a metallic screen, e.g. a titanium or stainless steel screen. In one example, the tissue growth promoting material from whichchronic fixation mechanism103 is fabricated is selected from the group of materials consisting of tubular-weave polyethylene velour, polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) mesh, and combinations thereof.

Although examplechronic fixation mechanism103 includes a generally rectangular shape, other examples according to this disclosure may include chronic fixation mechanisms with different shapes, including circular, oval, or irregular shapes. In some such examples, the attachment of the chronic fixation mechanism may differ from that described with reference to examplechronic fixation mechanism103. For example, a circular or oval shaped chronic fixation mechanism may be attached to the outer surface of the body of an IMD, e.g. an implantable sensor along the entire peripheral edge of the mechanism, like along the entire circumference of a circular shaped chronic fixation mechanism.

As noted above,temporary fixation mechanism102 andchronic fixation mechanism103 offixation device100 are configured to function in concert to anchorsensor38 within, e.g.,pulmonary artery39 ofpatient14. As such, in one example,chronic fixation mechanism103 is fabricated from a tissue growth promoting material that is designed to facilitate enough tissue in-growth into the chronic fixation mechanism by the timetemporary fixation mechanism102 substantially degrades, thereby chronically securingsensor38 in the lumen ofpulmonary artery39.

FIG. 4 is a flowchart illustrating an example method of securing an IMD within the body of a patient according to this disclosure. The method ofFIG. 4 includes arranging the IMD adjacent to tissue at a target location within the body (200), temporarily anchoring the IMD to the tissue with a temporary fixation mechanism (202), and chronically anchoring the IMD to the tissue with a chronic fixation mechanism (204). The temporary fixation mechanism includes a biodegradable material and is configured to secure the IMD to the tissue after implantation until the temporary fixation mechanism biodegrades. The chronic fixation mechanism is configured to promote sufficient tissue growth such that the mechanism chronically secures the IMD to the tissue before the temporary fixation mechanism biodegrades.

The example method ofFIG. 4 is described with reference tosensor38 andexample fixation device100 ofFIGS. 3A and 3B. In particular, the method ofFIG. 4 is described with reference toFIGS. 5A-5D, which illustrate the placement ofsensor38 withfixation device100 in the lumen ofpulmonary artery39 ofpatient14. It is noted, however, that the techniques illustrated by the example method ofFIG. 4 for securing an IMD within the body of a patient may be applied to other IMDs using different fixation devices in accordance with this disclosure. For example, the techniques of the method ofFIG. 4 may be applied to an implantable leadless pacemaker placed in one of the chambers of the heart, e.g. the right ventricle, and secured in the body using a fixation device that includes a temporary fixation mechanism and a chronic fixation mechanism which differ in configuration and/or composition to exampletemporary fixation mechanism102 andchronic fixation mechanism103 ofFIGS. 3A, 3B, and 5A-5D.

As noted above,FIGS. 5A-5D illustrate the placement ofsensor38 withfixation device100 in the lumen ofpulmonary artery39 ofpatient14.FIG. 5A illustrates the arrangement ofsensor38 in the lumen ofpulmonary artery39 ofpatient14 and the temporary anchoring of the sensor withtemporary fixation mechanism102.FIG. 5B illustrates the beginning of tissue growth into the tissue growth promoting sheet of material of whichchronic fixation mechanism103 is comprised.FIG. 5C illustrates the transition betweentemporary fixation mechanism102 andchronic fixation mechanism103 in which the tissue growth intochronic fixation mechanism103 has advanced sufficiently to holdsensor38 in place withouttemporary fixation mechanism102, and showingsuch mechanism102 having begun to degrade. Finally,FIG. 5D illustratessensor38 chronically anchored to the endothelium, in the lumen ofpulmonary artery39 ofpatient14 withchronic fixation mechanism103, andtemporary fixation mechanism102 no longer present, i.e. fully degraded.

Referring the example method ofFIG. 4 andFIG. 5A,sensor38 is arranged at a target location within the body ofpatient14, which, in the example ofFIG. 5A, is a location within the lumen ofpulmonary artery39.Sensor38, to whichfixation device100 is attached, may be delivered to the target location within the body ofpatient14 in a variety of ways. In one example,sensor38 is delivered to the target location withinpulmonary artery39 using a delivery catheter. The delivery catheter may be employed as part of, e.g., an endoscopic implantation system for guidingsensor38 to and implanting the sensor at the implantation location withinpatient14, e.g. inpulmonary artery39. In one example, the delivery catheter is directed through a vein intoright atrium26 ofpatient14, thenright ventricle28 and through the right ventricle outflow tract (RVOT) from theright ventricle28 through the pulmonary valve topulmonary artery39. The lumen of the delivery catheter may receivesensor38 and, in one example, a guide wire. The guide wire may be employed to stabilize and guide the placement ofsensor38 at the desired location within the lumen ofpulmonary artery39, and allow the sensor to be accurately placed in more tortuous vasculature. In one example, the catheter may include a guide wire lumen in which the guide wire is arranged. In such an example, the guide wire may be placed at a site distal to the target implant site withinpatient14, andsensor38 may be guided along the guide wire to the site of implant.

Regardless of the particular mode of delivery, oncesensor38 includingfixation device100 is delivered to the target location within the lumen ofpulmonary artery39, the sensor is temporarily anchored in the lumen with temporary fixation mechanism102 (202). As described above,temporary fixation mechanism102 may include an expandable and contractible stent. In one example,temporary fixation mechanism102 is biased into an expanded state.Sensor38 withfixation device100 includingtemporary fixation mechanism102 attached to the body of the sensor may be delivered to the location withinpulmonary artery39 withtemporary fixation mechanism102 in a contracted state, e.g. held in a contracted state within the lumen of the delivery catheter. Whensensor38 is arranged at the target location, the delivery catheter, or other containment vessel, e.g. a separate sheath, may be refracted to release the biasedtemporary fixation mechanism102 such that the stent springs into an expanded state to engagepulmonary artery39 and to push the side ofsensor38 includingchronic fixation mechanism103 against the endothelium ofpulmonary artery39, as illustrated inFIG. 5A. In this manner,temporary fixation mechanism102 temporarily anchorssensor38 within the lumen ofpulmonary artery39, so thatchronic fixation mechanism103 may begin to function to promote tissue growth leading to chronic fixation ofsensor38 to the wall ofpulmonary artery39. Additionally, in this manner, the biasing of temporary fixation mechanism may function to pushsensor38 andchronic fixation mechanism103 against the endothelium of pulmonary artery39 (or another vessel in which thesensor38 is placed) when in an expanded state.

Aftersensor38 includingfixation device100 has been arranged at the target location withinpulmonary artery39 and the sensor has been temporarily anchored withtemporary fixation mechanism102,fixation device100 goes through a transition from temporarily anchoring the sensor within the body ofpatient14 to chronically anchoring the sensor withchronic fixation mechanism103. In one example according to this disclosure, this transition from temporary to chronic fixation ofsensor38 within the body ofpatient14 is illustrated inFIGS. 5B and 5C.

InFIG. 5B,tissue growth120 intochronic fixation mechanism103 has begun. However,temporary fixation mechanism102 remains the primary mechanism by whichsensor38 is anchored to the endothelium, within the lumen ofpulmonary artery39. It should be noted that even if the same or substantially similar sheet of tissue growth promoting material is used for a chronic fixation mechanism according to this disclosure, the configuration of the chronic fixation mechanism with respect to the IMD may affect the function of the fixation mechanism.FIGS. 6A and 6B are schematic illustrations of two different connections betweenchronic fixation mechanism103 and an IMD,e.g. sensor38. As described above, examplechronic fixation mechanism103 includes a rectangular sheet of tissue growth promoting material with two parallel and generally opposing edges attached to the outer surface ofsensor38. In the example ofFIG. 6A, the two edges ofchronic fixation mechanism103 are attached to the body ofsensor38 such that the rectangular sheet is pulled taut to lay on the outer surface of the sensor. The arrangement ofFIG. 6A may require relatively less material forchronic fixation mechanism103 and may be less apt to entanglement with other structures during the placement ofsensor38 inpulmonary artery39. In the example ofFIG. 6B, however, the two edges ofchronic fixation mechanism103 are attached to the body ofsensor38 such that the rectangular sheet remains at least partially slack and at least a portion of the rectangular sheet is offset from the outer surface of the sensor. The arrangement ofFIG. 6B may facilitate more rapid and/or stronger anchoring ofsensor38 withinpulmonary artery39 because the space betweenchronic fixation mechanism103 and the outer surface of the sensor may allow tissue to grow through the sheet of material of whichchronic fixation mechanism103 is comprised and grow between the fixation mechanism and the sensor, thereby potentially more fully incorporating the chronic fixation mechanism and the sensor into the wall of the lumen ofpulmonary artery39.

Additionally, as noted above,chronic fixation mechanism103 may include a sheet of flexible fabric, or, in another example,chronic fixation mechanism103 may include a metallic screen, e.g. a titanium or stainless steel screen. In examples including a flexible fabric chronic fixation mechanism, such mechanism may not conform to a particular shape, but may, instead, be shaped based on external forces, e.g. gravity and/or tissue or fluids within the body of the patient. Such an example may be illustrated by the configuration ofchronic fixation mechanism103 inFIG. 6B. In examples including a metallic screen chronic fixation mechanism, however, such mechanism may be elastically deformed into different shape configurations, including, e.g. the pedestal shape of chronic fixation mechanism105 illustrated inFIG. 6C. Example metallic screen chronic fixation mechanism105 ofFIG. 6C may be fabricated from a number of biocompatible metals including, e.g. titanium and stainless steel. Additionally, metallic screen chronic fixation mechanism105 is, in one example, a sheet of material that forms a pedestal shaped frame. As such, chronic fixation mechanism105 may be connected tosensor38 in a manner similar to that described above with reference tochronic fixation mechanism103. In some examples, metallic screen chronic fixation mechanism105 may be coated with a material that is configured to promote tissue growth into and around pores in the sheet of screen.

In another example, however, a chronic fixation mechanism according to this disclosure may include a block of material formed into, e.g. a pedestal shape and connected to an IMD. For example,FIG. 6D is a cross-sectional view ofsensor38 withchronic fixation mechanism109 connected to one side ofsensor38. In this example, instead of being formed from a sheet of material that forms a frame in a pedestal shape,chronic fixation mechanism109 is formed from a block of material that forms a substantially solid pedestal connected tosensor38. In such examples,chronic fixation mechanism109 may be formed with surface features, e.g. surface variations and/or pores, or may be coated with a material configured to promote tissue growth to chronically anchorsensor38 to tissue within a patient, or even may have attached, in some manner, a flexible, growth-promoting fabric, similar to that discussed in regard toFIGS. 6A-6B.

Referring again to the method ofFIG. 4 andFIGS. 5A-5D,FIG. 5C illustrates the transition between temporary and chronic fixation ofsensor38 withinpulmonary artery39 in whichtissue growth120 intochronic fixation mechanism103 has advanced andtemporary fixation mechanism102 has begun to degrade. And, finally, inFIG. 5D,sensor38 is chronically anchored withinpulmonary artery39 by chronic fixation mechanism103 (204) viatissue growth120 having advanced further into the chronic fixation mechanism to secure the sensor to the wall of the lumen ofpulmonary artery39, at which pointtemporary fixation mechanism102 may have substantially degraded. The time period over which the transition between temporary and chronic fixation ofsensor38 within the body ofpatient14 illustrated inFIGS. 5B and 5C occurs may be days, weeks, or months, e.g., depending on the safety profile applicable for a given device and/or implant site. However, as noted above,temporary fixation mechanism102 andchronic fixation mechanism103 are configured to function in concert such thatenough tissue growth120 intochronic fixation mechanism103 occurs before or, at the least, by the timetemporary fixation mechanism102 substantially degrades.

Although the foregoing examples have been described with reference to exampletemporary fixation mechanism102 including the expandable and contractible stent illustrated inFIGS. 3A, 3B, and 5A-5D, in other examples a temporary fixation mechanism according to this disclosure may include a number of different configurations. For example,FIG. 7 illustratessensor38 anchored withinblood vessel300 with an example fixation device including expandabletemporary fixation mechanism302 andchronic fixation mechanism304. In one example,chronic fixation mechanism304 may be substantially similar tochronic fixation mechanism103 described above. Additionally,chronic fixation mechanism304 may be connected tosensor38 in the manner described with reference to eitherFIG. 6A or 6B such that the sheet of tissue growth promoting material is either pulled taut to lay against or is slack such that part of the sheet is offset from the outer surface of the sensor, or in a manner like that ofFIG. 6C or 6D, with a pedestal and any number of means of chronic fixation, metal screen coated or uncoated, or solid material, coated or uncoated, or either screen or solid material with fabric, or any combination of the above that maximizes tissue ingrowth and chronic attachment integrity.

Temporary fixation mechanism302 includes a cylindrical, expandable and contractible stent that is configured to temporarily anchorsensor38 withinvessel300. The biodegradable materials and properties oftemporary fixation mechanism302 may be substantially similar to those oftemporary fixation mechanism102 described above. In the example ofFIG. 7,temporary fixation mechanism302 includes a mesh stent with a plurality of material segments each of which is pivotally joined at either end to another segment at a vertex. The material segments of whichtemporary fixation mechanism302 is comprised may be constructed from various biodegradable materials that are configured to temporarily anchorsensor38 withinblood vessel300 and degrade over time untilchronic fixation mechanism304 chronically anchors the sensor within the vessel. In one example,temporary fixation mechanism302 is expandable and contractible by rotation of the material segments with respect to each other at the plurality of vertices at which the segments are pivotally joined. Astemporary fixation mechanism302 contracts, the material segments rotate such that the angle of each segment with respect to a longitudinal axis of the temporary fixation mechanism decreases, which in turn decreases the diameter and increases the overall length of the lead member. Conversely, astemporary fixation mechanism302 expands, the material segments rotate such that the angle of each segment with respect to the longitudinal axis of the temporary fixation mechanism increases, which in turn increases the diameter and decreases the overall length of the lead member. In another example,sensor38 may be mounted tofixation mechanism302 in a similar manner to that ofFIG. 7, except that it is mounted on the inside offixation mechanism302, rather than the outside. Either of these approaches may work well, depending on other conditions, but the intent of both is to holdchronic fixation mechanism304 against the endothelium ofvessel300.

FIG. 8 is a plan view ofsensor38 includingexample fixation device400 withtemporary fixation mechanism402 andchronic fixation mechanism403.Sensor38 also includesbattery104, sensingelements106, andTCC electrodes108. In the example ofFIGS. 3A and 3B, sensingelements106 and other electronic components ofsensor38, e.g., a TCC system, is powered bybattery104.Sensor38, components thereof andfixation device400 may be configured and function in substantially similar manner as described with reference to the example ofFIGS. 3A and 3B, and 5A-5D. However,temporary fixation mechanism402 is connected tosensor38 such thatsensor38 is arranged withintemporary fixation mechanism402. In this example, part oftemporary fixation mechanism402 is connected to the same side ofsensor38 to whichchronic fixation mechanism403 is connected. In this example and similar arrangements of an IMD and fixation devices according to this disclosure, tissue growth promoted bychronic fixation mechanism403 may occur aroundtemporary fixation mechanism402, which may thereafter biodegrade to leavesensor38 anchored to tissue of a patient bychronic fixation mechanism403.

In some examples according to this disclosure, a temporary fixation mechanism may include a mechanism for securing an IMD that differs from an expandable and contractible stent, such as those described with reference totemporary fixation mechanisms102 ofFIGS. 3A and 3B, 302 ofFIG. 7, and 402 ofFIG. 8. A temporary fixation mechanism according to this disclosure may include a mechanism that is configured to secure an IMD at a target location by penetrating or pinching tissue adjacent the location. For example, a temporary fixation mechanism according to this disclosure may include one or a combination of barbs, tines, hooks, harpoons, or threaded, helical, or other anchors that are configured to penetrate or pinch tissue to secure an IMD within the body of a patient. As with the example stents described above, such temporary fixation mechanisms are fabricated from a biodegradable material and are configured to anchor the IMD to the tissue of the patient after implantation until the temporary fixation mechanism biodegrades in accordance with the examples described above. Examples of a number of types of anchors which may be employed as temporary fixation mechanisms in examples according to this disclosure are illustrated inFIGS. 9A-9J.

Although fixation techniques according to this disclosure are described in the context of cardiac devices, and, in particular, sensors for cardiac systems, the examples disclosed herein may also be employed to place other types of implantable medical devices. In some examples, a fixation device including temporary and chronic fixation mechanisms in accordance with this disclosure may be employed with medical devices that deliver therapy via a medical lead. For example, a fixation device in accordance with the disclosed examples may be employed in a neurostimulation system for spinal cord, gastric, pelvic floor, or deep brain stimulation delivered via one or more electrical stimulation leads. In another example, the examples disclosed herein may be used in conjunction with implantable fluid delivery systems, e.g., implantable drug pumps that are configured to deliver therapeutic fluids via a catheter. A fixation device in accordance with this disclosure may also be employed with an implantable microstimulator. For example, a fixation device in accordance with this disclosure may be employed with an implantable leadless pacemaker configured to be implanted, e.g., within the right ventricle of a patient's heart to deliver one or more of pacing, cardioversion, and/or defibrillation to the patient.

In addition, systems according to this disclosure are not limited to treatment of a human patient. In alternative examples,therapy system10 may be implemented in non-human patients, e.g., primates, canines, equines, pigs, and felines. These other animals may undergo clinical or research therapies that may benefit from the subject matter of this disclosure.

Some techniques described in this disclosure, including those attributed toIMD16,programmer24,sensor38, or various constituent components, may be implemented, at least in part, in hardware, software, firmware or any combination thereof. For example, various aspects of the techniques may be implemented within one or more processors, including one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components, embodied in programmers, such as physician or patient programmers, stimulators, image processing devices or other devices. The term “processor” or “processing circuitry” as used herein may generally refer to any of the foregoing logic circuitry, alone or in combination with other logic circuitry, or any other equivalent circuitry.

Such hardware, software, firmware may be implemented within the same device or within separate devices to support the various operations and functions described in this disclosure. In addition, any of the described units, modules or components may be implemented together or separately as discrete but interoperable logic devices. Depiction of different features as modules or units is intended to highlight different functional aspects and does not necessarily imply that such modules or units must be realized by separate hardware or software components. Rather, functionality associated with one or more modules or units may be performed by separate hardware or software components, or integrated within common or separate hardware or software components.

When implemented in software, the functionality ascribed to the systems, devices and techniques described in this disclosure may be embodied as instructions on a computer-readable storage medium such as random access memory (RAM), read-only memory (ROM), non-volatile random access memory (NVRAM), electrically erasable programmable read-only memory (EEPROM), FLASH memory, magnetic data storage media, optical data storage media, or the like. The instructions may be executed to support one or more aspects of the functionality described in this disclosure. The term “memory” as used herein may generally refer to any of the foregoing types of computer-readable storage media, alone or in combination with other logic circuitry, or any other equivalent circuitry. The computer-readable storage medium may be nontransitory.

Various examples have been described. These and other examples are within the scope of the following claims.

Claims (35)

The invention claimed is:

1. An implantable medical device (IMD) comprising:

a body containing electronics;

a fixation device connected to the body of the device, wherein the fixation device comprises:

a temporary fixation mechanism comprising a biodegradable material and configured to anchor the IMD within a blood vessel of a patient after implantation until the temporary fixation mechanism biodegrades; and

a chronic fixation mechanism overlaying a first side of the body and configured to promote tissue growth along the first side of the body that anchors the IMD within the blood vessel of the patient before the temporary fixation mechanism biodegrades such that the chronic fixation mechanism is configured to more permanently anchor the IMD to the blood vessel than the temporary fixation mechanism,

wherein the temporary fixation mechanism is configured to anchor the IMD within the blood vessel such that the first side of the body including the chronic fixation mechanism is arranged against endothelium of the blood vessel, and

wherein the chronic fixation mechanism comprises a sheet of tissue growth promoting material configured to be connected to the IMD housing and configured to promote tissue growth into the material to secure the IMD within the blood vessel of the patient before the temporary fixation mechanism biodegrades, wherein the sheet of tissue growth promoting material comprises a rectangular sheet of tissue growth promoting material defined by four edges, and wherein a first edge is attached to the outer surface of the IMD housing and a second edge generally parallel to and offset from the first edge is attached to the outer surface of the IMD housing.

2. The IMD ofclaim 1, wherein the temporary fixation mechanism comprises a biodegradable stent configured to be connected to at least one of a first side or a second side of the body of the IMD generally opposite the first side such that the stent is configured to push the first side of the body of the IMD including the chronic fixation mechanism against the endothelium of the blood vessel.

3. The IMD ofclaim 1, wherein the blood vessel of the patient comprises at least one of the right or the left first branches of the pulmonary artery, a systemic vessel, a brain vessel, or a renal vessel.

4. The IMD ofclaim 1, wherein the temporary fixation mechanism comprises at least one of polyglycolic acid (PGA), poly lactic acid (PLA), polydioxanone (PDS), polyanhydrides, trimethylene carbonate, polyhydroxybutyrate (PHB), polyhydroxyvalerate (PHV), polycaprolactone, polyorthoesters, polyaminoacids, polycyanocrylates, and polyphosphazenes.

5. The IMD ofclaim 1, wherein the temporary fixation mechanism comprises a biodegradable material selected from the group consisting of polyesters, polyurethanes, and combinations thereof.

6. The IMD ofclaim 1, wherein the temporary fixation mechanism comprises a biodegradable material selected from the group consisting of polyglycolic acid (PGA), polylactic acid (PLA), and combinations thereof.

7. The IMD ofclaim 1, wherein the temporary fixation mechanism comprises a biodegradable material selected from the group consisting of magnesium, magnesium alloys, iron, iron alloys, and combinations thereof.

8. The IMD ofclaim 1, wherein the temporary fixation mechanism comprises a biodegradable material configured to substantially degrade by a first time sufficient to allow enough tissue growth to the chronic fixation mechanism to secure the IMD within the blood vessel of the patient.

9. The IMD ofclaim 1, wherein the sheet of tissue growth promoting material is configured overlay at least part of an outer surface of the body.

10. The IMD ofclaim 1, wherein the sheet of tissue growth promoting material comprises a sheet of flexible fabric.

11. The IMD ofclaim 1, wherein the first and second edges of the rectangular sheet of tissue growth promoting material are attached to the body of the IMD such that the rectangular sheet of tissue growth promoting material is pulled taut to lay on the outer surface of the body of the IMD.

12. The IMD ofclaim 1, wherein the first and second edges of the rectangular sheet of tissue growth promoting material are attached to the body of the IMD such that the rectangular sheet of tissue growth promoting material remains at least partially slack and at least a portion of the rectangular sheet of tissue growth promoting material is offset from the outer surface of the body of the IMD.

13. The IMD ofclaim 1, wherein the sheet of tissue growth promoting material is selected from the group consisting of tubular-weave polyethylene velour, polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) mesh, and combinations thereof.

14. The IMD ofclaim 1, wherein the sheet of tissue growth promoting material comprises a sheet of metallic screen.

15. The IMD ofclaim 14, wherein the sheet of metallic screen comprises at least one of titanium and stainless steel.

16. The IMD ofclaim 1, wherein the electronics include a least one of a battery, a telemetry module, sensing elements and a signal generator configured to generate electrical stimulation.

17. An assembly comprising:

an implantable medical device (IMD) comprising a housing containing electronics; and

a fixation device for the IMD, the fixation device comprising:

a temporary fixation mechanism connected to the IMD, wherein the temporary fixation mechanism comprises a biodegradable material and is configured to anchor the IMD within a blood vessel of a patient after implantation until the temporary fixation mechanism biodegrades; and

a chronic fixation mechanism overlaying a first side of the IMD housing, wherein the chronic fixation mechanism is configured to promote tissue growth along the first side of the IMD housing that anchors the IMD within the blood vessel before the temporary fixation mechanism biodegrades such that the chronic fixation mechanism is configured to more permanently anchor the IMD to the blood vessel than the temporary fixation mechanism,

wherein the chronic fixation mechanism comprises a sheet of tissue growth promoting material configured to be connected to the IMD housing and configured to promote tissue growth into the material to secure the IMD within the blood vessel of the patient before the temporary fixation mechanism biodegrades, wherein the sheet of tissue growth promoting material comprises a rectangular sheet of tissue growth promoting material defined by four edges, and wherein a first edge is attached to the outer surface of the IMD housing and a second edge generally parallel to and offset from the first edge is attached to the outer surface of the IMD housing, and wherein the temporary fixation mechanism is configured to anchor the IMD within the blood vessel such that the first side of the IMD housing, including the chronic fixation mechanism, is arranged against endothelium of the blood vessel.

18. The assembly ofclaim 17, wherein the temporary fixation mechanism comprises a biodegradable stent configured to be connected to at least one of the first side or a second side of the IMD housing such that the stent is configured to push the first side of the IMD housing, including the chronic fixation mechanism, against the endothelium of the blood vessel.

19. The assembly ofclaim 17, wherein the blood vessel of the patient comprises at least one of the right or the left branches of the pulmonary artery, a systemic vessel, a brain vessel, or a renal vessel.

20. The assembly ofclaim 17, wherein the temporary fixation mechanism comprises at least one of polyglycolic acid (PGA), polylactic acid (PLA), polydioxanone (PDS), polyanhydrides, trimethylene carbonate, polyhydroxybutyrate (PHB), polyhydroxyvalerate (PHV), polycaprolactone, polyorthoesters, polyaminoacids, polycyanocrylates, and polyphosphazenes.

21. The assembly ofclaim 17, wherein the temporary fixation mechanism comprises a biodegradable material selected from the group consisting of polyesters, polyurethanes, and combinations thereof.

22. The assembly ofclaim 17, wherein the temporary fixation mechanism comprises a biodegradable material selected from the group consisting of polyglycolic acid (PGA), polylactic acid (PLA), and combinations thereof.

23. The assembly ofclaim 17, wherein the temporary fixation mechanism comprises a biodegradable material selected from the group consisting of magnesium, magnesium alloys, iron, iron alloys, and combinations thereof.

24. The assembly ofclaim 17, wherein the temporary fixation mechanism comprises a biodegradable material configured to substantially degrade by a first time sufficient to allow enough tissue growth to the chronic fixation mechanism to secure the IMD within the blood vessel of the patient.

25. The assembly ofclaim 17, wherein the sheet of tissue growth promoting material is configured to at least part of an outer surface of the IMD housing.

26. The assembly ofclaim 17, wherein the sheet of tissue growth promoting material comprises a sheet of flexible fabric.

27. The assembly ofclaim 17, wherein the first and second edges of the rectangular sheet of tissue growth promoting material are attached to the IMD housing such that the rectangular sheet of tissue growth promoting material is pulled taut to lay on the outer surface of the IMD housing.

28. The assembly ofclaim 17, wherein the first and second edges of the rectangular sheet of tissue growth promoting material are attached to the IMD housing such that the rectangular sheet of tissue growth promoting material remains at least partially slack and at least a portion of the rectangular sheet is offset from the outer surface of the IMD housing.

29. The assembly ofclaim 17, wherein the sheet of tissue growth promoting material is selected from the group consisting of tubular-weave polyethylene velour, polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) mesh, and combinations thereof.

30. The assembly ofclaim 17, wherein the sheet of tissue growth promoting material comprises a sheet of metallic screen.

31. The assembly ofclaim 30, wherein the sheet of metallic screen comprises at least one of titanium and stainless steel.

32. The assembly ofclaim 30, wherein the sheet of metallic screen forms a pedestal protruding from the first side of the housing such that the housing of the IMD is offset from the endothelium of the blood vessel.

33. The assembly ofclaim 17, wherein the electronics include a least one of a battery, a telemetry module, sensing elements and a signal generator configured to generate electrical stimulation.

34. A method of securing an implantable medical device (IMD) within the body of a patient, the method comprising:

arranging the IMD at a target location within a blood vessel of the patient, wherein the IMD comprises a housing containing electronics;

temporarily anchoring the IMD within the blood vessel with a temporary fixation mechanism comprising a biodegradable material, wherein the temporary fixation mechanism is configured to secure the IMD within the blood vessel after implantation until the temporary fixation mechanism biodegrades; and

chronically anchoring the IMD within the blood vessel with a chronic fixation mechanism overlaying a first side of the IMD housing and configured to promote tissue growth along the first side of the IMD housing that secures the IMD within the blood vessel before the temporary fixation mechanism biodegrades, wherein the chronic fixation mechanism is configured to more permanently anchor the IMD to the blood vessel than the temporary fixation mechanism,

wherein the temporary fixation mechanism is configured to anchor the IMD within the blood vessel such that the first side of the IMD housing including the chronic fixation mechanism is arranged against endothelium of the blood vessel, and

wherein the chronic fixation mechanism comprises a sheet of tissue growth promoting material configured to be connected to the IMD housing and configured to promote tissue growth into the material to secure the IMD within the blood vessel of the patient before the temporary fixation mechanism biodegrades, wherein the sheet of tissue growth promoting material comprises a rectangular sheet of tissue growth promoting material defined by four edges, and wherein a first edge is attached to the outer surface of the IMD housing and a second edge generally parallel to and offset from the first edge is attached to the outer surface of the IMD housing.

35. The method ofclaim 34, wherein the electronics include a least one of a battery, a telemetry module, sensing elements and a signal generator configured to generate electrical stimulation.

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